In recent years composite materials have become increasingly popular for use in a variety of aerospace applications because of their durability and relative light weight. Several fiber fabric preforms can be used in composite manufacturing, such as woven fabric, braided fabric, and non-crimp fabric. The use of these fiber fabric preforms can allow for automation in the manufacturing process, and can provide a lower-cost and more robust fabrication method for composite components than existed previously.
Of the fiber fabric preforms, woven fabric is generally the most widely used and least expensive. The fibers of woven fabrics typically display a perpendicular (0° and 90°) orientation that has to be cut and rotated if the fibers need to be placed at any bias angles for manufacturing purposes. This disadvantage often results in increased material waste and reduction in the automation of the component fabrication process. Compared to woven fabric, braided fabrics can allow for more design flexibility because the fibers can be oriented at bias angles. However, braided fabric is generally more difficult to produce, and therefore, more expensive than woven fabric. Moreover, braided fabrics having the fibers at bias angles can support only a defined maximum amount of applied tension during component fabrication beyond which the fiber architecture of the material will undesirably distort.
In an effort to address some of the foregoing issues, multiaxial non-crimp fabric (NCF) has recently started being used to make composite components. As used herein, NCF refers to any fabric preform that can be made by stacking one or more layers of unidirectional fibers and then stitching the layers together. The stitching yarns serve as a manufacturing aid that hold the layers together and allow for handling of the fabric. The yarns are consistent throughout the fabric and are not used for structural function.
NCF can be less costly than woven fabrics because there is less material waste and automation can be used to accelerate the component fabrication process. Additionally, because of the lack of interweaving fibers and inherent efficiency in the fabrication process, NCF can be less costly to make than braided fabric. However, compared to weaves and braids, which can be manufactured to have a built-in contoured shape using a specially designed fabric take-up mandrel, NCF generally needs to be produced as a flat sheet or roll. Because of this, the conformability of NCF is generally not as good as that achieved using braids or weaves, and therefore, can be more difficult to conform to a contoured geometry without developing wrinkles.
Accordingly, there remains a need for methods for making non-crimp fabric having improved conformability and contoured components made using such methods.